Rock drill bit with hard m etal cutting insert



Sept- 14, 1 D. w. HAGLUND ROCK DRILL BIT WITH HARD METAL CUTTING INSERT Fild July 2, 1951 INVENTOR;

ATTORNEYS.

Patented Sept. 14, 1954 ATENT OFFICE ROCK DRILL BIT WITH HARD DIETAL CUTTING INSERT Didrik Wilhelm Haglund assignor to Sandviken Sandviken, Sweden, s Jernverks Aktiebolag,

Sandviken, Sweden, a corporation of Sweden Application July 2, 1951, Serial No. 234,852 Claims priority, application Sweden July 4, 1950 12 Claims. .1

The present invention relates to rock drills of the type having wear resisting inserts of hard metal carbides such as sintered tungsten carbide and to inserts for incorporation therein.

It has been proposed to use inserts of cemented tungsten carbides for the cutting edges and other wearing surfaces of percussion type rock drills and this has been done with some success. However, these hard metal carbides themselves are made in varying degrees of hardness and wear resistance. Those of the harder and more wear resistant grades, containing less bonding metal such as cobalt, are more brittle and liable to fracture and chipping in service than are the tougher grades of lesser hardness which contain a higher percentage of bonding metal and are thus tougher and more resistant to chipping and fracture, though less resistant to wear.

It has been desired to utilize the harder grades of such hard metal carbides in rock drills to make them more long lived and resistant to wear both at the cutting edges and at the periphery to prevent reduction in the diameter thereof, but it has not been practical to do so due to the fact that the harder grades do not withstand the severe impact stresses to which the drills are subjected in service and the drills accordingly are unsatisfactory due to excessive chipping, fracture and breaking up of the inserts.

Attempts to overcome these difiiculties have been made, such as by making blades in sections of two different grades of hard metal carbides with a center portion of a tougher grade and end portions exposed at the periphery of the drill of a harder grade to reduce peripheral wear and loss of diameter. However, these attempts have not proven successful because the inserts are still too brittle and ruptures often occur at the junction between the softer and harder portions.

It accordingly is an object of the invention to provide rock drills and novel hard metal carbide inserts therefor which incorporate the harder grades of cemented metal carbides, to take the wear at critical points, but which at the same time are resistant to chipping and fracture. The achievement of this object is made possible by the provision of a compound insert in which a plug or core formed of a harder grade of cemented metal carbide is mounted in a hole or recess in a cutting insert formed of a less hard but tougher grade of cemented metal carbide and secured therein by brazing or welding. It has been proven in practice that such an insert substantially eliminates the difficulties due to chipping and rupture of the hard metal carbide inserts as previously employed.

In the preferred construction according to the invention, the inserts comprise a solid core of a harder grade of cemented metal carbide and a surrounding tube or shell of a tougher grade thereof, the two bodies being united by brazing or welding and then mounted in a drill bit with the ends of the core exposed and constituting peripheral Wear resisting surfaces. The outer surrounding shell being softer and tougher protects the hard and more brittle core.

The difference between the temperature coeificients of the two grades of material is very small, the softer grade due to the higher percentage of bonding metal being slightly greater and resulting during the brazing operation in an increased gripping effect of the shell on the core. However, the strains caused by brazing are minute and are completely absorbed by the brazed joint between the shell and the core.

Other objects and advantages of the invention will become apparent during the course of the following detailed description with reference to the accompanying drawings. In the drawings:

Fig. 1 is a perspective view of a rock drill bit incorporating a hard metal carbide cutting insert embodying the invention,

Fig. 2 is a side elevation of an insert of the type shown in Fig. 1,

Fig. 3 is an end view thereof,

Fig. 4 is a side elevation of a modified form of insert embodying the invention,

Fig. 5 is an end view thereof,

Fig. 6 is an end view illustrating a further modification, and,

Fig. 7 is a side elevation of a cutter insert embodying a further modification.

Referring now more particularly to the drawings, l is a drill bit formed with a transverse bore 2 adjacent the tip thereof within which is secured a hard metal carbide insert 3 embodying the invention, the rounded periphery of the latter being exposed through the open side of the bore 2 at the apex of the bit to constitute the cutting edge of the bit. The insert is secured in place by brazing and the area forming the cutting edge is exposed by grinding opposite sides of the drill bit to taper the same as indicated at preferably after the insert is secured in position, although the grinding of the drill bit may be accomplished before mounting the insert, thereby forming the slot through which the insert is exposed. The outlet for delivery of flushing liquid to the bit through the usual hollow drill stem is indicated at 5.

The hard metal carbide insert 3 shown mounted in the bit I comprises a hard metal carbide core 6, as seen more particularly in Figs. 2 and 3, formed of a harder grade of cemented metal carbide, such as tungsten carbide, containing lesser amounts of bonding metal such as cobalt, and a surrounding "shell or jacket '1, formed of tougher grade'of cemented metal carbide, containing ai greater amount of bonding metal, thus being tougher and more resistant to fracture and chipping than the core 6. The core 6 is united to the shell '5 by a thin layer of brazing metal indicated at 8. In forming the insert, the core 6 and shell 7 are sintered separately of the desired composition, respectively, to make the very hard and relatively brittle core 6" and the relatively tough though less hard shell orsleeve. '1; After formation the core is slipped into the shell and the two are united by brazing or welding. The

finished insert is then slipped into the bore. 2'

in the drill bit, and united thereto by brazing or Welding, using lowermelting brazing metal than thatused' in uniting the inseitpai'ts so as not to remelt the same.

The compound hard metal carbide insert 3 is the same length as the diameter of the drill bit and is exposed at the ends of the bore 2 so that the ends of the hard core 6, which is more resistant to wear than either the metal of the drill bit or the shell 7, are exposed to contact the walls of the bore hole in service, thereby gauging the size of the hole and preventing loss of diameter which otherwise would result from wearing due to abrasion of the periphery of the drill bit or the ends of the tough grade of hard metal carbide forming thecutting edge of the bit in the absence of the harder core 6.

Instead of forming the insert with the shell and core coextensive with each other as illustrated in Figs. 1, 2 and 3, the harder inserts may be formed as plugs secured in the ends of a tougher cemented carbide cutter blade. Such an insert is shown'in Figs; 4 and 5 wherein a cutter blade H! of a tough grade of cemented carbide is formed with a hole H of substantial diameter in each end thereof. Within the hole I l is seated a plug 62, of a harder grade of cemented carbide, secured therein by a uniting layer of brazing or welding metal [3. In this instance the blade it is preferably formed with a fiat bottom and sides at right angles thereto and a chisel edge Hi forming the cutting edge of the bit. It i will be understood that such an insert is secured by brazing in a rectangular open groove in the bit in which it is mounted.

Another modification of the invention is illustrated in Fig. 6, wherein an insert in the form of.

a cutter blade I5 formed of a tough grade of cemented carbide is provided with a plurality of small diameter holes It in the ends thereof within each of which is secured, by brazing or welding, a plug ii of a harder grade of cemented carbide.

In the forms of the invention illustrated in Figs. 4, 5 and 6 it will be observed that the tougher grade of hard metal carbide forming the body of the blade and cutting edge will resist percussive strains and forces, whereas the harder grade plugs i2 and ii being exposed at the ends of the blade will gauge the hole and resist reduction in diameter of the bit.

A further modification of the invention is shown in Fig. 7 wherein the cutting edge of a hard metal carbide insert is formed of a harder and more brittle grade than could otherwise be utilized for this purpose. In this case the insert blade 20 is formed of a tough grade of cemented'carbide.

and provided with a plurality of closely spaced vertical bores or holes 2| axially centered with respect to and opening on the chisel edge 22 thereof. The bores 2! extend deep into the blade to or adjacent the bottom'or back thereof and are filled by preformed plugs 23 of a harder, more brittle grade of cemented carbide, which plugs are united to the body of the blade by brazingor welding. Where the insert blade, as shown, has a slightly convex cutting edge, the harder metal carbide core pieces may be, and preferably are, disposed at a slight angle with respect to each otherwith their axes along the radii of 'theedge.

While preferred embodiments of the invention have been shown and described by way of illustratidn; it will be understood that various other modifications may be resorted to without departing from the spiritiof the invention within the scope of the appended claims.

I claim:

1. In a rock drill; a drill bit having an open ended transverse channel, a cutter insert mounted in said channel, said insertcomprising a body formedof a relatively 'tough'grade of'cemented metal carbide havinga tubularhole of substantially circular cross section therein-opening on at least one wear receiving surface of said body and a plug of a relatively harder grade of cemented metal carbide mounted in said hole and united to said body by brazing and having an end surface thereof exposed 'atthe' open end of the hole in said body to constitute awear resistant surface, said tough grade of cemented metal carbide having a greater coefiicient of expansion than said harder grade.

2. A rock drill as claimed in claim 1, in which the body of the cutter insertis an open ended tube and the plug is a-core extending from end to end of-said tube with'the ends'of the core forming peripheralwear resistant surfaces on said bit.

3. A'rock drill as defined in claim 1, in which the'body of the cutter-insert is ablade having a hole in each endth'ereof and a plug of the harder grade metal carbide is'mounted in each of said holes with the exposed ends forming peripheral wear resisting surfaces onsaid bit.

4. A rock drill as defined in claim '1, in which the body of the cutter insert isblade having a plurality of closely spaced vertical bores opening at the cutting edge thereof and a'plug' of harder grade metal carbide is mounted in each of said bores.

5. A rock drill as defined in claim 1, in which thebody of the'cutter insert is a blade having a plurality. of holes in each end thereof and a plug of the harder grade metal carbideis mounted. in each of said holes with'the exposed ends thereof forming peripheral wear resisting-surfaces on said bit.

6. A cutting'insert for rock drill bits comprising an elongated body portion formed of a tough grade of cemented metal carbide having a tubular hole' of substantially circular cross section therein'opening' on at least onewear. receiving surface of said body and 'a'plug of a harder grade of cemented metalcarbide seated in said hole and united thereto by brazing to said body with an end face exposed at the outer end of said hole constituting a wear resistant surface, said tough grade of cemented metal carbide having a greater coefficient of expansion than said harder grade.

71A cutting insert for rock drills comprising an elongated body portion formedof a tough grade of cemented metal carbide having a tubular hole of substantially circular cross section in each end thereof and a plug of harder grade of cemented metal carbide seated in the hole at each end of said body and united thereto by brazing with the outer end face of each of said plugs exposed to constitute a Wear resisting surface, said tough grade of cemented metal carbide having a greater coefficient of expansion than said harder grade.

8. A cutting insert for rock drills comprising an elongated body portion formed of a tough grade of cemented metal carbide having a plurality of tubular bore holes of substantially circular cross section in opposite ends thereof and a plug of a harder grade of cemented metal carbide seated in each of said bore holes and united to said body by brazing, the outer ends of each of said plugs being exposed and constituting Wear resisting surfaces at the ends of said body, said tough grade of cemented metal carbide having a greater coefiicient of expansion than said harder grade.

9. A cutting insert for rock drills comprising an elongated blade member formed of a tough grade of cemented metal carbide, said blade member having a chisel edge and a row of tubular bore holes of substantially circular cross section opening at one end at said chisel edge, and a plug of a harder grade cemented metal carbide seated in each of said bore holes and united to said blade by brazing, each of said plugs having an outer exposed end constituting a wear receiving surface at said chisel edge, said tough grade of cemented metal carbide having a greater coefficient of expansion than said harder grade.

10. A cutting insert for rock drills comprising a tubular shell formed of a tough grade of cemented metal carbide and a core formed of a harder grade of cemented metal carbide filling said shell and united thereto by brazing, the end faces of said core being exposed and constituting wear resisting surfaces, said tough grade of cemented metal carbide having a greater coefiicient of expansion than said harder grade.

11. A rock drill as defined in claim 1 in which the side surfaces of the plug are surrounded by said body.

12. A cutter insert as defined in claim 6 in which the side surfaces of the plug are surrounded by the body.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,949,050 Howard et a1 Feb. 2'7, 1934 2,019,934 Schroter Nov. 5, 1935 2,032,328 Reedy Feb. 25, 1936 2,121,202 Killgore June 21, 1938 2,243,608 Schuarte May 27, 1941 FOREIGN PATENTS Number Country Date 634,743 Great Britain Mar. 29, 1950 686,029 Germany Dec. 30, 1939 886,835 France July 19, 1943 

